Aqueous silica-containing composition

ABSTRACT

The present invention relates to an aqueous silica-containing composition comprising an anionic organic polymer having at least one aromatic group and anionic silica-based particles. The aqueous silica-containing composition contains the anionic organic polymer having at least one aromatic group and the anionic silica-based particles in an amount of at least 0.01% by weight of the total weight of the aqueous silica-containing composition. The aqueous silica-containing composition contains substantially no cellulose-reactive sizing agent and the anionic organic polymer having at least one aromatic group is not an anionic naphthalene sulphonate formaldehyde condensate. The invention further relates to methods for the preparation of the aqueous silica-containing composition and the use of the aqueous silica-composition as a drainage and retention aid in a process for the production of paper. The invention also relates to a process for the production of paper from an aqueous suspension containing cellulosic fibres, and optionally filler, in which the aqueous silica-containing composition and at least one charged organic polymer are added to the cellulosic suspension.

The present patent application is a divisional of U.S. patentapplication Ser. No. 10/326,320, filed on Dec. 20, 2002, which claimspriority of U.S. Provisional Patent Application Ser. No. 60/342,306,filed on Dec. 21, 2001.

The present invention relates to an aqueous silica-containingcomposition comprising an anionic organic polymer having at least onearomatic group and anionic silica-based particles. The invention furtherrelates to a method for the preparation of the aqueous silica-containingcomposition, uses of the aqueous silica-containing composition and apapermaking process.

BACKGROUND OF THE INVENTION

In the papermaking art, an aqueous suspension containing cellulosicfibres, and optionally fillers and additives, referred to as stock, isfed into a headbox which ejects the stock onto a forming wire. Water isdrained from the stock through the forming wire so that a wet web ofpaper is formed on the wire. The formed paper web is dewatered and driedin the drying section of the paper machine. Drainage and retention aidsare conventionally introduced into the stock in order to facilitatedrainage and to increase adsorption of fine particles onto thecellulosic fibres in such a way that the fine particles are retainedwith the fibres on the wire.

U.S. Pat. No. 4,388,150 discloses a binder in papermaking comprising acomplex of cationic starch and colloidal silicic acid to produce a paperhaving increased strength and improved levels of retention of addedminerals and papermaking fines.

U.S. Pat. No. 4,750,974 discloses a coarcervate binder for use inpapermaking comprising a tertiary combination of a cationic starch, ananionic high molecular weight polymer and a dispersed silica.

U.S. Pat. No. 5,368,833 discloses silica sols containing aluminiummodified silica particles with high specific surface area and a highcontent of microgel.

U.S. Pat. No. 5,567,277 discloses a composition comprising an aqueouscellulosic furnish, a high molecular weight cationic polymer and ananionic polymer comprising modified lignin.

U.S. Pat. No. 6,022,449 discloses the use of water-dispersiblepolyisocyanates with anionic and/or potentially anionic groups andcationic and/or potentially cationic compounds in paper finishing.

EP 0 418 015 A1 discloses an active sizing composition containing anaqueous emulsion in combination with an anionic dispersant oremulsifier. By using anionic polyacrylamide, anionic starch or colloidalsilica the anionic charge density in the sizing composition can beextended.

U.S. Pat. No. 5,670,021 refers to a process for the production of paperby forming and dewatering a suspension of cellulose, wherein thedewatering takes place in the presence of an alkali metal silicate and aphenolic resin added at the same point into the suspension.

U.S. Pat. No. 6,033,524 discloses a method for increasing retention anddrainage of filling components in a paper making furnish in a papermaking process comprising adding to the furnish a slurry of fillingcomponents, also containing a phenolic enhancer.

U.S. Pat. No. 6,315,824 pertains to a dispersed composition comprising ahydrophobic phase and an aqueous phase, the composition being stabilisedby a cationic colloidal coacervate stabilising agent, the coacervatestabilising agent comprising an anionic component and a cationiccomponent.

EP 0,953,680 A1 refers to a process for the production of paper from ssuspension comprising adding to the suspension a cationic organicpolymer.

U.S. Pat. No. 5,185,062 discloses a papermaking process including thesteps of adding to the papermaking slurry a high molecular weightcationic polymer and then a medium molecular weight anionic polymer.

U.S. Pat. No. 4,313,790 refers to a process for the production of paperwhich consists of the addition to the papermaking furnish of kraftlignin or modified kraft lignin and poly(oxyethylene).

U.S. Pat. No. 6,165,259 relates to an aqueous dispersion containing adispersant and a disperse phase containing a hydrophobic material, thedispersant comprising an anionic compound and a cationic compound.

It would be advantageous to be able to provide drainage and retentionaids with improved performance. It would also be advantageous to be ableto provide retention and drainage aids with good storage stability. Itwould further be advantageous to be able to provide a papermakingprocess with improved drainage and/or retention performance.

THE INVENTION

According to the present invention it has unexpectedly been found thatan improved drainage and/or retention effect of a cellulosic suspensionon a wire can be obtained by using an aqueous silica-containingcomposition comprising at least one anionic organic polymer with atleast one aromatic group and anionic aggregated or microgel formedsilica-based particles. The aqueous silica-containing composition isuseful in processes for production of paper from all types of stocks, inparticular stocks having high contents of salts (high conductivity) andcolloidal substances. The aqueous silica-containing composition is alsouseful in papermaking processes with a high degree of white waterclosure, i.e. extensive white water recycling and limited fresh watersupply. Hereby the present invention makes it possible to increase thespeed of the paper machine and to use a lower dosage of additives togive a corresponding drainage and/or retention effect, thereby leadingto an improved papermaking process and economic benefits.

The terms “drainage and retention aid”, as used herein, refer to one ormore components, which when added to an aqueous cellulosic suspension,give better drainage and/or retention than is obtained when not addingthe said one or more components. All types of stocks, in particularstocks having high contents of salts (high conductivity) and colloidalsubstances will obtain better drainage and retention performances by theaddition of the composition according to the present invention. This isimportant in papermaking processes with a high degree of white waterclosure, i.e. extensive white water recycling and limited fresh watersupply.

In accordance with the present invention there is provided an aqueoussilica-containing composition comprising an anionic organic polymerhaving at least one aromatic group and anionic silica-based particlescomprising aggregated or microgel formed silica-based particles. Theaqueous silica-containing composition contains the anionic organicpolymer having at least one aromatic group and total amount of anionicsilica-based particles in an amount of at least 0.01% by weight based onthe total weight of the aqueous silica-containing composition. Thecomposition contains substantially no cellulose-reactive sizing agentand the said anionic organic polymer is not an anionic naphthalenesulphonate formaldehyde condensate.

There is further provided an aqueous silica-containing compositionobtainable by mixing an anionic organic polymer having at least onearomatic group with an aqueous alkali stabilised silica sol containingaggregated or microgel formed silica-based particles having an S-valuein the range of from about 5 up to about 50%. The obtained aqueoussilica-containing composition contains the anionic organic polymerhaving at least one aromatic group and total amount of silica-basedparticles in an amount of at least 0.01% by weight based on the totalweight of the aqueous silica-containing composition. The compositioncontains substantially no cellulose-reactive sizing agent and that saidanionic organic polymer is not anionic naphthalene sulphonateformaldehyde condensate.

There is further provided a method for preparation of an aqueoussilica-containing composition which comprises mixing in the presence ofsubstantially no cellulose-reactive sizing agent an anionic organicpolymer having at least one aromatic group with aggregated or microgelformed silica-based particles to provide an aqueous silica-containingcomposition containing the anionic organic polymer having at least onearomatic group and total amount of silica-based particles in an amountof at least 0.01% by weight, based on the total weight of the aqueoussilica-containing composition with the proviso that the anionic organicpolymer having at least one aromatic group is not an anionic naphthalenesulphonate formaldehyde condensate.

There is further provided a method for preparation of an aqueoussilica-containing composition which comprises mixing an anionic organicpolymer having at least one aromatic group and a charge density of atleast 0.1 meq/g of dry polymer, with aggregated or microgel formedsilica-based particles to provide an aqueous silica-containingcomposition containing the anionic organic polymer having at least onearomatic group and total amount of silica-based particles in an amountof at least 0.01% by weight, based on the total weight of the aqueoussilica-containing composition, with the proviso that the anionic organicpolymer having at least one aromatic group is not an anionic naphthalenesulphonate formaldehyde condensate.

There is further provided a method for preparation of an aqueoussilica-containing composition which comprises desalinating an aqueoussolution of an anionic organic polymer having at least one aromaticgroup, mixing in the desalinated anionic organic polymer having at leastone aromatic group with aggregated or microgel formed silica-basedparticles to provide an aqueous silica-containing composition containingthe anionic organic polymer having at least one aromatic group and totalamount of silica-based particles in an amount of at least 0.01% byweight, based on the total weight of the aqueous silica-containingcomposition with the proviso that the anionic organic polymer having atleast one aromatic group is not an anionic naphthalene sulphonateformaldehyde condensate.

There is further provided an aqueous silica-containing compositionobtainable by the methods according to the invention.

The invention further relates to the use of the aqueoussilica-containing composition of the invention, as flocculating agent incombination with at least one cationic organic polymer in the productionof pulp and paper and for water purification.

According to the invention there is further provided a process for theproduction of paper from a suspension containing cellulosic fibres, andoptionally fillers, comprising adding to the suspension at least onecationic organic polymer and an aqueous silica-containing compositionaccording to the invention.

The aqueous silica-containing composition comprises at least one anionicorganic polymer with at least one aromatic group, which is not ananionic naphthalene sulfonate formaldehyde condensate. The aromaticgroup of the anionic polymer can be present in the polymer backbone orin a substituent group that is attached to the polymer backbone (mainchain). Examples of preferably aromatic groups include aryl, aralkyl andalkaryl groups and derivatives thereof, e.g. phenyl, tolyl, naphthyl,phenylene, xylylene, benzyl, phenylethyl and derivatives of thesegroups. The anionically charged groups can be present either in theanionic polymer or in the monomers used for preparing the anionicpolymer. The anionically charged groups can either be groups carrying ananionic charge or acid groups carrying an anionic charge when dissolvedor dispersed in water. These groups are herein collectively beingreferred to as anionic groups, such as phosphate, phosphonate, sulphate,sulphonic acid, sulphonate, carboxylic acid, carboxylate, alkoxide andphenolic groups, i.e. hydroxy-substituted phenyls and naphthyls. Groupscarrying an anionic charge are usually salts of an alkali, alkalineearth metals or ammonia.

Anionic polymers containing one or more aromatic groups according to theinvention can preferably be selected from the group consisting ofstep-growth polymers, chain-growth polymers, polysaccharides andnaturally occurring aromatic polymers. The term “step-growth polymer”,as used herein, refers to a polymer obtained by step-growthpolymerisation, also being referred to as step-reaction polymer andstep-reaction polymerisation, respectively. Preferably the anionicpolymer is a step-growth polymer. The anionic polymers according to theinvention can be linear, branched or cross-linked. Preferably theanionic polymer is water-soluble or water-dispersible.

Examples of suitable anionic step-growth polymers according to thepresent invention include condensation polymers, i.e. polymers obtainedby step-growth condensation polymerisation, e.g. condensates of analdehyde such as formaldehyde with one or more aromatic compoundscontaining one or more anionic groups, and optional other comonomersuseful in the condensation polymerisation such as urea and melamine.Examples of suitable aromatic compounds containing anionic groupscomprises compounds containing anionic groups such as phenolic compoundse.g. phenol, resorcinol and derivatives thereof, aromatic acids andsalts thereof.

Examples of suitable anionic step-growth polymers according to thepresent invention include addition polymers, i.e. polymers obtained bystep-growth addition polymerisation, e.g. anionic polyurethanes preparedfrom a monomer mixture comprising aromatic isocyanates and/or aromaticalcohols. Examples of suitable aromatic isocyanates includediisocyanates, e.g. toluene-2,4- and 2,6-diisocyanates anddiphenylmethane-4,4′-diisocyanate. Examples of suitable aromaticalcohols include dihydric alcohols, i.e. diols, e.g. bisphenol A, phenyldiethanol amine, glycerol monoterephthalate and trimethylolpropanemonoterephthalate. Monohydric aromatic alcohols such as phenol andderivatives thereof may also be employed. The monomer mixture can alsocontain non-aromatic isocyanates and/or alcohols, usually diisocyanatesand diols, for example any of those known to be useful in thepreparation of polyurethanes. Examples of suitable monomers containinganionic groups include the monoester reaction products of triols, e.g.trimethylolethane, trimethylolpropane and glycerol, with dicarboxylicacids or anhydrides thereof, e.g. succinic acid and anhydride,terephthalic acid and anhydride, such as glycerol monosuccinate,glycerol monoterephthalate, trimethylolpropane monosuccinate,trimethylolpropane monoterephthalate, N,N-bis-(hydroxyethyl)-glycine,di-(hydroxymethyl)propionic acid,N,N-bis-(hydroxyethyl)-2-aminoethanesulfonic acid, and the like,optionally and usually in combination with reaction with a base, such asalkali and alkaline earth metal hydroxides, e.g. sodium hydroxide,ammonia or an amine, e.g. triethylamine, thereby forming an alkali,alkaline earth metals or ammonium counter-ion.

Examples of suitable anionic chain-growth polymers according to theinvention include anionic vinyl addition polymers obtained from amixture of vinylic or ethylenically unsaturated monomers. The mixture ofvinylic or ethylenically unsaturated monomers comprises at least onemonomer having an aromatic group and at least one monomer having ananionic group. Usually the monomers are co-polymerised with non-ionicmonomers such as acrylate- and acrylamide-based monomers. Examples ofsuitable anionic monomers include (meth)acrylic acid and paravinylphenol (hydroxy styrene).

Examples of suitable anionic polysaccharides with at least one aromaticgroup include starches, guar gums, cellulose derivatives, chitins,chitosans, glycans, galactans, glucans, xanthan gums, pectins, mannans,dextrins, preferably starches, and guar gums, preferably starchesincluding potato, corn, wheat, tapioca, rice, waxy maize and barley,preferably potato. The anionic groups in the polysaccharide can benative and/or introduced by chemical treatment. The aromatic groups inthe polysaccharide can be introduced by chemical methods known in theart.

Examples of suitable (modified) naturally occurring aromatic anionicpolymers of this invention include lignosulphonates, Kraft lignins,oxylignins, and tannin extracts i.e. naturally occurring polyphenolicsubstances that are obtained from the sulphite or sulphate pulpprocesses or from extracts of bark.

The weight average molecular weight of the anionic polymer can varywithin wide limits dependent on, inter alia, the type of polymer used,and usually it is at least about 500, preferably above about 800 andpreferably above about 1,000. The upper limit is not critical; it can beabout 10,000,000, usually 1,000,000, preferably 500,000, preferably200,000 and most preferably 100,000.

The anionic polymer can have a degree of anionic substitution (DS_(A))varying over a wide range dependent on, inter alia, the type of polymerused. DS_(A) is usually from 0.01 to 2.0, preferably from 0.02 to 1.8and preferably from 0.025 to 1.5; and the degree of aromaticsubstitution (DS_(Q)) can be from 0.001 to 1.0, usually from 0.01 to0.8, preferably from 0.02 to 0.7 and more preferably from 0.025 to 0.5.In case the anionic polymer contains cationic groups, the degree ofcationic substitution (DS_(C)) can be, for example, from 0 to 0.2,preferably from 0 to 0.1 and more preferably from 0 to 0.05, the anionicpolymer having an overall anionic charge. Usually the anionic charge ofthe anionic polymer is within the range of from 0.1 to 10.0 meq/g of drypolymer, preferably from 0.2 to 6.0 meq/g, and more preferably from 0.5to 4.0 meq/g.

The aqueous silica-containing composition according to the inventionalso comprises anionic aggregated or microgel formed silica-basedparticles i.e. particles based on SiO₂, preferably formed bypolymerising silicic acid, encompassing both homopolymers andcopolymers. Optionally the silica-based particles can be modified andcontain other elements, e.g. amine, aluminium and/or boron, which can bepresent in the aqueous phase and/or in the silica-based particles.

Examples of suitable aggregated or microgel formed silica-basedparticles include colloidal silica, colloidal aluminium-modified silicaor aluminium silicate, and different types of polysilicic acid andmixtures thereof, either alone or in combination with other types ofanionic silica-based particles. In the art, polysilicic acid is alsoreferred to as polymeric silicic acid, polysilicic acid microgel,polysilicate and polysilicate microgel, which are all encompassed by theterm polysilicic acid used herein. Aluminium-containing compounds ofthis type are commonly referred to as polyaluminosilicate andpolyaluminosilicate microgel including colloidal aluminium-modifiedsilica and aluminium silicate.

The anionic silica-based particles are in the colloidal range ofparticle size. This state comprises particles sufficiently small not tobe affected by gravitational forces but sufficiently large not to showmarked deviation from the properties of typical solutions, i.e. averageparticle size significantly less than 1 μm. The anionic silica-basedparticles have an average particle size preferably below about 50 nm,preferably below about 20 nm and more preferably in the range of fromabout 1 to about 50 nm, most preferably from about 1 up to about 10 nm.As conventional in silica chemistry, the particle size refers to theaverage size of the primary particles, which may be aggregated ornon-aggregated.

Preferably, the silica-based particles have a specific surface arealarger than 50 m²/g, preferably larger than 100 m²/g. The specific areacan be up to 1700 m²/g, preferably up to 1300 m²/g and usually in therange from 300 to 1300 m²/g, preferably from 500 to 1050 m²/g. Thespecific surface area can be measured by means of titration with NaOHaccording to the method described by Sears, Analytical Chemistry28(1956), 12, 1981-1983 or in U.S. Pat. No. 5,176,891. The given areathus represents the average specific surface area of the particles.

The total weight of the anionic organic polymer having at least onearomatic group and total amount of anionic silica-based particlescontained in the aqueous silica-containing composition is at least 0.01%by weight, calculated on the total weight of the aqueoussilica-containing composition, preferably at least 0.05% by weight, morepreferably at least 0.1% by weight. Preferably the concentration of theanionic organic polymer having at least one aromatic group and theanionic silica-based particles is within the range of 1 to 45% byweight, preferably within the range of 2 to 35% by weight, mostpreferably 5 to 30% by weight.

The aqueous silica-containing composition can have an anionic chargedensity of at least 0.1 meq/g, usually the charge is within the range offrom 0.1 to 10 meq/g, preferably within the range of from 0.1 to 8meq/g, preferably within the range of from 0.1 to 6 meq/g, and mostpreferably within the range of from 0.2 to 4 meq/g.

The aqueous silica-containing composition according to the inventioncontains substantially no cellulose-reactive sizing agent. Bysubstantially no means that less than or equal to 10% by weight,preferably less than 5%, preferably less than 1% by weight ofcellulose-reactive sizing agent is present in the aqueoussilica-containing composition. Most preferably there is nocellulose-reactive sizing agent in the aqueous silica-containingcomposition. Even more preferably, the aqueous silica-containingcomposition according to the invention contains substantially no sizingagent, preferably, contains no sizing agent.

The present invention relates further to a method for preparation of anaqueous silica-containing composition. The two components are preferablystirred together. The anionic organic polymer having at least onearomatic group can be added to an aqueous sol containing thesilica-based particles or the silica-based particles can be added to anaqueous solution of anionic organic polymer having at least one aromaticgroup. The aqueous solution of anionic organic polymer having at leastone aromatic group may be desalinated or deionisated. The desalinationor deionisation can be carried out with dialysis, membrane filtration,ultrafiltration, reversed osmosis or ion exchange or the like. It ispreferred that the desalination or deionisation is carried out by theuse of ultra-filtration or dialysis. The pH of an aqueous solution ofanionic organic polymer may be adjusted to the pH of the silica-basedparticles, prior to or after mixing the aqueous solution with thesilica-based particles. The pH can be adjusted to at least pH 8.0,preferably at least 9.0, preferably at least 9.5, preferably within therange of 9.0 to 11.0.

The anionic organic polymer having at least one aromatic group to bemixed with the silica-based particles can have an anionic charge densityof at least 0.1 meq/g, usually within the range of from 0.1 to 10.0meq/g of dry polymer, preferably within the range of from 0.2 to 6.0 andpreferably within the range of from 0.5 to 4.0.

The silica-based particles, preferably anionic, to be mixed with theanionic organic polymer can have the previous mentioned properties.Preferably the silica-based particles are contained in a sol. The solmay have an S-value in the range of from 5 to 80%, preferably from 5 to50%, preferably from 8 to 45%, and most preferably from 10 to 30%.Calculation and measuring of the S-value can be performed as describedby Iler & Dalton in J. Phys. Chem. 60(1956), 955-957. The S-valueindicates the degree of aggregate or microgel formation and a lowerS-value is indicative of a higher degree of aggregation.

Preferably the silica-based particles have a molar ratio Si₂O:Na₂O lessthan 60, usually within the range 5 to 60, and preferably within therange from 8 to 55.

The aqueous silica-containing composition obtained by any of the methodsaccording to the invention, contains preferably a total weight of theanionic organic polymer having at least one aromatic group and totalamount of anionic silica-based of at least 0.01% by weight, calculatedon the total weight of the aqueous silica-containing composition,preferably at least 0.05% by weight, more preferably at least 0.1% byweight. Preferably the concentration of anionic organic polymer havingat least one aromatic group and anionic silica-based particles is withinthe range of 1 to 45% by weight, preferably within the range of 2 to 35%by weight, most preferably 5 to 30% by weight.

The products prepared by any of these methods shows improved drainageand retention properties, and also a better storage stability andtherefore a better drainage and retention aid performance when storedbecause it has a longer shelf life.

The mixing procedure of above mention methods is preferably carried outin the presence of substantially no cellulose-reactive sizing agent. Bysubstantially no means that less or equal to 10% by weight, preferablyless than 5%, preferably less than 1% by weight of cellulose-reactivesizing agent is present. Most preferably there is no cellulose-reactivesizing agent present. The mixing procedure may also be carried out inthe presence of substantially no sizing agent, or in the presence of nosizing agent.

The present invention further relates to a process for the production ofpaper from an aqueous suspension containing cellulosic fibres. Theprocess comprises adding to the suspension a cationic organic polymerand the aqueous silica-containing composition of the invention. Thecationic organic polymer according to the invention can be linear,branched or cross-linked. Preferably the cationic polymer iswater-soluble or water-dispersible.

Examples of suitable cationic polymers include synthetic organicpolymers, e.g. step-growth polymers and chain-growth polymers, andpolymers derived from natural sources, e.g. polysaccharides.

Examples of suitable cationic synthetic organic polymers include vinyladdition polymers such as acrylate- and acrylamide-based polymers, aswell as cationic poly(diallyl dimethyl ammonium chloride), cationicpolyethylene imines, cationic polyamines, polyamidoamines andvinylamide-based polymers, melamine-formaldehyde and urea-formaldehyderesins.

Examples of suitable polysaccharides include starches, guar gums,cellulose derivatives, chitins, chitosans, glycans, galactans,, glucans,xanthan gums, pectins, mannans, dextrins, preferably starches and guargums. Examples of preferably starches include potato, corn, wheat,tapioca, rice, waxy maize, barley, etc.

Cationic starches and cationic acrylamide-based polymers are preferredpolymers according to the invention, and they can be used singly,together with each other or together with other polymers, particularlypreferred are cationic starches and cationic acrylamide-based polymershaving at least one aromatic group.

The cationic organic polymers can have one or more hydrophobic groupsattached to them. The hydrophobic groups can be aromatic groups, groupscomprising aromatic groups or non-aromatic groups, preferably thehydrophobic groups comprise aromatic groups. The hydrophobic group canbe attached to a heteroatom, e.g. nitrogen or oxygen, the nitrogenoptionally being charged, which heteroatom, it can be attached to thepolymer backbone, for example via a chain of atoms. The hydrophobicgroup may have at least 2 and usually at least 3 carbon atoms,preferably from 3 to 12 and preferably from 4 to 8 carbon atoms. Thehydrophobic group is preferably a hydrocarbon chain.

Preferable dosages counted as dry substance based on dry pulp andoptional filler, of the cationic polymer in the system is from 0.01 to50 kg/t (kg/tonne, “metric ton”) of, preferably from 0.1 to 30 kg/t andmost preferably from 1 to 15 kg/t.

Preferable dosages counted as dry substances based on dry pulp andoptional filler, of the aqueous silica-containing composition definedabove in the system are from 0.01 to 15 kg/t, preferably from 0.01 to 10kg/t calculated as an anionic organic polymer having at least onearomatic group and anionic silica-based particles, and most preferablyfrom 0.05 to 5 kg/t.

Suitable mineral fillers of conventional types may be added to theaqueous cellulosic suspension according to the invention. Examples ofsuitable fillers include kaolin, china clay, titanium dioxide, gypsum,talc and natural and synthetic calcium carbonates such as chalk, groundmarble and precipitated calcium carbonate (PCC).

Further additives that are conventional in papermaking can of course beused in combination with the chemicals according to the invention, forexample anionic trash catchers (ATC), wet strength agents, dry strengthagents, optical brightening agents, dyes, aluminium compounds, etc.Examples of preferably aluminium compounds include alum, aluminates,aluminium chloride, aluminium nitrate, and polyaluminium compounds, suchas polyaluminium chlorides, polyaluminium sulphates, polyaluminiumcompounds containing chloride and/or sulphate ions, polyaluminiumsilicate sulphates, and mixtures thereof. The polyaluminium compoundsmay also contain other anions than chloride ions, for example anionsfrom sulfuric acid, phosphoric acid, or organic acids such as citricacid and oxalic acid. When employing an aluminium compound in thepresent process, it is usually preferably to add it to the stock priorto the polymer component and micro- or nano-particulate material.Preferably addition levels of aluminium containing compounds is at least0.001 kg/t, preferably from 0.01 to 5 kg/t and more preferably from 0.05to 1 kg/t, calculated as Al₂O₃ based on dry pulp and optional filler.

Examples of suitable anionic trash catchers include cationic polyamines,polymers or copolymers of quaternary amines, or aluminum containingcompounds.

The process of this invention is used for the production of paper. Theterm “paper”, as used herein, include not only paper and the productionthereof, but also other web-like products, such as for example board andpaperboard, and the production thereof. The invention is particularlyuseful in the manufacture of paper having grammages below 150 g/m²,preferably below 100 g/m², for example fine paper, newspaper, lightweight coated paper, super calendered paper and tissue.

The process can be used in the production of paper from all types ofstocks, both wood containing and woodfree. The different types ofsuspensions of cellulose-containing fibres and the suspensions shouldpreferably contain at least 25% by weight and preferably at least 50% ofweight of such fibres, based on dry substance. The suspensions comprisefibres from chemical pulp such as sulphate, sulphite and organosolvpulps wood-containing or mechanical pulp such as thermomechanical pulp,chemo-thermomechanical pulp, refiner pulp and groundwood pulp, from bothhardwood and softwood, and can also be based on recycled fibres,optionally from de-inked pulps, and mixtures thereof. Preferably thestock is a wood containing stock, which have high contents of salts(high conductivity).

The chemicals according to the present invention can be added to theaqueous cellulosic suspension, or stock, in conventional manner and inany order. It is usually preferably to add the cationic polymer to thestock before adding the aqueous silica-containing composition, even ifthe opposite order of addition may be used. It is further preferred toadd the cationic polymer before a shear stage, which can be selectedfrom pumping, mixing, cleaning, etc., and to add the aqueoussilica-containing composition after that shear stage.

The aqueous silica-containing composition can be used as a flocculationagent in the treatment of water for the production of drinking water oras an environmental treatment of waters for instance in lakes. Thecomposition can also be used as flocculation agent in the treatment ofwastewater or waste sludges.

The invention is further illustrated in the following examples, whichare not intended to limit the scope thereof. Parts and % relate to partsby weight and % by weight, respectively, and all solutions are aqueous,unless otherwise stated. The units are metric.

EXAMPLE 1

Drainage performance was evaluated by means of a Dynamic DrainageAnalyser (DDA), available from Akribi, Sweden. The drainage time wasmeasured on a set volume of stock through a wire when removing a plugand applying vacuum to that side of the wire opposite to the side onwhich the stock is present.

Retention performance was evaluated by means of a nephelometer bymeasuring the turbidity of the filtrate, the white water, obtained bydraining the stock. The trurbidity was measure in NTU (NephelometricTurbidity Units).

The test stock was wood containing with a pH 7.2, the conductivity ofthe stock was 5.0 mS/cm, and the consistency was 1.42 g/l. The stock wasstirred in a baffled jar at a speed of 1500 rpm throughout the test.

In the example a cationic polymer was added to the stock before theaqueous compositions according to the invention or the anionicreference. The cationic polymer was a cationic starch (C1) obtained byquarternisation of native potato starch with 3-chloro-2-hydroxypropyldimethyl benzyl ammonium chloride to 0.5% N was added followed by 45seconds of stirring, and then the anionic aqueous composition was added,followed by 15 seconds stirring before drainage.

Aqueous compositions according to the invention containing anionicpolyurethane and colloidal silica were measured to evaluate theirdrainage and retention performance. All samples were diluted to 0.5% ofsolids before the evaluation of drainage properties. The anionicpolyurethane (P1) is based on an anionic polyurethane of 15% solids,produced from glyceryl monostearate (GMS) and toluolyl diisocyanate(TDI), which forms a pre-polymer, which is reacted with dimethylolpropionic acid (DMPA), with 30 mol % of GMS is replaced by DPMA/N-methyldiethanol amine (N-MDEA). The colloidal silica sol (S1) is of the typedescribed in U.S. Pat. No. 5,447,604 having a molar ratio SiO₂:Na₂O of10, specific surface area of 870 m²/g, S-value of 35% and silica contentof 10.0% by weight. The drainage time measured on the stock withaddition of 20 kg/t of C1 was 29 seconds and the turbidity was measuredto 44 NTU. All additions are calculated as dry on dry stock. Thedrainage times derived from the different additions to the stock of theaqueous composition of the invention are summarised in Table 1. TABLE 1Drainage time (sec)/Turbidity (NTU) at dosage of Sample Ratio 4 kg/t 6kg/t 8 kg/t 10 kg/t S1 19.7/35 16.9/31 15.6/30 16.0/29 P1 17.7/3415.3/33 14.0/32 13.9/32 S1/P1 4:1 17.3/33 14.0/30 13.5/28 14.0/27 S1/P11:1 16.4/34 13.6/30 13.0/28 13.1/28 S1/P1 1:4 16.5/33 13.9/31 13.3/2912.9/29The drainage times and turbidity for the composition S1/P1 show thatwhen the two components (S1 and P1) are added as a composition they havea synergistic improvement on the drainage and retention performance.

EXAMPLE 2

The aqueous compositions according to the invention containing anionicpolyurethane (P2) based on an anionic polyurethane of 19% solids,produced from TDI and phenyl diethanol amine PDEA, which forms thepre-polymer, which is reacted with a mixture of DMPA and N-MDEA and ofwhich 30 mol % of PDEA is replaced by DPMA/N-MDEA, and a colloidalsilica (S2) having a molar ratio SiO₂:Na₂O of 20, specific surface areaof 700 m²/g, S-value of 32% and silica content of 15.0%, were evaluatedfor drainage and retention performance. All the samples were diluted to0.5% solids before the drainage and retention evaluation, which wasperformed exactly in the same manner as in Example 1 and with the samecationic starch in the same stock. The drainage time measured on thestock with addition of 20 kg/t of C1 was 27 seconds and the turbiditywas measured to 45 NTU. All additions are calculated as dry on drystock. The drainage times derived from the different additions to thestock of the aqueous composition of the invention are summarised inTable 2. TABLE 2 Drainage time (sec)/Turbidity (NTU) at dosage of SampleRatio 2 kg/t 4 kg/t 6 kg/t 8 kg/t S2 21.0/— 15.7/— 12.4/— 12.9/— P221.8/44 18.0/39 12.9/31 12.0/29 S2/P2 4:1 21.0/40 15.5/31 12.0/2810.4/27 S2/P2 1:1 — 13.8/30 11.0/27  9.8/27 S2/P2 1:4 — 13.3/32 11.0/2910.3/27

EXAMPLE 3

In this example the test stock was SC-furnish (furnish for SuperCalandered paper) with a pH 7.6, the conductivity of the stock was 0.5mS/cm, and the consistency was 1,49 g/l. The stock was stirred in abaffled jar at a speed of 1500 rpm throughout the test. C1 was added tothe stock in an amount of 20 kg/t (kg/tonne) in each test. The drainagetime measured on the stock without any additives was 30 seconds and theturbidity was 98 NTU, the drainage time on the stock with addition of C1only was 14.8 seconds and the turbidity was measured to 52 NTU. Theanionic polyurethane used in this example was an anionic polyurethane(P3) of 15% solids, produced from GMS and TDI, which forms apre-polymer, which is reacted DMPA and the colloidal silica (S3)described in U.S. Pat. No. 5,368,833 was a silica sol having a molarratio SiO₂:Na₂O of 45, specific surface area of 850 m²/g, S-value of 20%and a silica content of 8.0%, and was modified with aluminium to 0.3%Al₂O₃.

The performance of the aqueous composition according to the inventionwas compared to the performance of the components added separately. Inall tests C1 was added to the stock followed by 45 seconds of stirring,then the composition S3/P3 was added followed by 15 seconds of stirring.When the components were added separately the first component was addedfollowed by 30 seconds of stirring and the second components was addedfollowed by 15 seconds of stirring. All additions are calculated as dryon dry stock. The drainage times derived from the different additions tothe stock are summarised in Table 3. TABLE 3 Drainage time(sec)/Turbidity (NTU) at dosage of Sample Ratio 1 kg/t 2 kg/t 3 kg/t 4kg/t C1 + S3 — — — 10.2/56 C1 + P3 13.9/54 13.0/55 12.0/56 13.0/55 C1 +S3/P3 1:1 12.6/52 11.4/51 10.0/58 10.0/55 C1 + S3/P3 3:1 12.2/52 11.1/5410.7/55 10.4/55 C1 + S3/P3 1:3 12.9/52 12.1/55 11.6/54 — C1 + S3 + P31:1 — — — 12.4/53 C1 + P3 + S3 1:1 — — — 12.4/55

EXAMPLE 4

The aqueous compositions according to the invention containing a 10%solution of an anionic lignosulphonate (LS1), which is the sodium saltof sulphonated and carboxylated Kraft lignin derived from soft wood,having a dry matter of 89.0% by weight, pH of 10.5, a sodium content of9.5%, and a total sulphur content of 5.4%, wherein sulphur is bound to4.2%, or a 10% solution anionic lignosulphonate (LS2), which is a sodiumoxylignin derived from fermented spruce wood sulphite liquor, having adry matter of 93.0% by weight, pH of 8.5, a sodium content of 8%, andsulphur content of 3%, and colloidal silica S1, were evaluated fordrainage and retention performance. All the samples were diluted to 0.5%solids before the drainage evaluation. The drainage time measured on thestock with addition of 20 kg/t of C1 was 29 seconds and the turbiditywas measured to 44 NTU. All additions are calculated as dry on drystock. The drainage times derived from the different additions to thestock of the aqueous composition of the invention are summarised inTable 4. TABLE 4 Drainage time (sec)/Turbidity (NTU) at dosage of SampleRatio 2 kg/t 4 kg/t 6 kg/t 8 kg/t 10 kg/t 12 kg/t S1 23.5/38 19.7/3516.9/31 15.6/30 16.0/29 — LS1 — 21.9/35 18.8/34 17.5/33 17.2/32 — LS2 —22.5/— 19.9/36 17.9/35 17.8/34 18.5/— S1/LS1 4:1 — 18.5/— 15.3/2914.4/26 14.5/25 — S1/LS1 1:1 — 18.8/— 15.5/30 13.1/30 12.8/31 — S1/LS24:1 — 18.4/— 15.1/31 13.2/28 12.5/27 12.4/25 S1/LS2 1:1 — 19.2/— 15.8/3313.8/28 12.8/25 12.1/26

1. A process for the production of paper from a suspension containingcellulosic fibres, and optionally fillers, comprising adding to thesuspension at least one cationic organic polymer and an aqueoussilica-containing composition comprising an anionic organic polymerhaving at least one aromatic group and aggregated or microgel formedanionic silica-based particles, the aqueous silica-containingcomposition containing the anionic organic polymer having at least onearomatic group and total amount of anionic silica-based particles in anamount of at least 0.01% by weight based on the total weight of theaqueous silica-containing composition, with the proviso that thecomposition contains substantially no cellulose-reactive sizing agentand the anionic organic polymer having at least one aromatic group isnot an anionic naphthalene sulphonate formaldehyde condensate.
 2. Theprocess according to claim 1 wherein the cationic organic polymer iscationic starch or cationic polyacrylamide.
 3. The process according toclaim 1 wherein the cationic organic polymer has at least one aromaticgroup.
 4. The process according to claim 2 wherein the cationic organicpolymer has at least one aromatic group.
 5. The process according toclaim 1 wherein the silica-based particles have a specific surface areafrom about 300 to about 1300 m²/g.
 6. The process according to claim 1wherein the silica-based particles have an average particle size rangingfrom about 1 nm up to about 10 nm.
 7. The process according to claim 1wherein pH of the aqueous solution of the anionic organic polymer havingat least one aromatic group is adjusted to a pH of at least 8 prior tomixing with the silica-based particles.
 8. The process according toclaim 1 wherein the anionic organic polymer having at least one aromaticgroup polymer is a polyurethane, lignosulphonate, Kraft lignin oroxylignin.
 9. The process according to claim 1 wherein the aqueoussilica-containing composition has a negative charge density within therange of from 0.1 to 6 meq/g.
 10. The process according to claim 1 withthe proviso that the composition contains substantially no sizing agent.11. A process for the production of paper from a suspension containingcellulosic fibres, and optionally fillers, comprising adding to thesuspension at least one cat ionic organic polymer and an aqueoussilica-containing composition obtainable by mixing an anionic organicpolymer having at least one aromatic group with an aqueous alkalistabilised silica sol containing aggregated or microgel formedsilica-based particles having an S-value in the range of from about 5 upto about 50%, to provide an aqueous silica-containing compositioncontaining the anionic organic polymer having at least one aromaticgroup and total amount of silica-based particles in an amount of atleast 0.01% by weight, based on the total weight of the aqueoussilica-containing composition, with the proviso that the compositioncontains substantially no cellulose-reactive sizing agent and that theanionic organic polymer having at least one aromatic group is not ananionic naphthalene sulphonate formaldehyde condensate.
 12. The processaccording to claim 12 wherein the cationic organic polymer is cationicstarch or cationic polyacrylamide.
 13. The process according to claim 12wherein the cationic organic polymer has at least one aromatic group.14. The process according to claim 12 wherein the cationic organicpolymer having at least one aromatic group.
 15. The process according toclaim 12 wherein the silica-based particles have a specific surface areafrom about 300 to about 1300 m²/g.
 16. The process according to claim 12wherein the silica-based particles have an average particle size rangingfrom about 1 nm up to about 10 nm.
 17. The process according to claim 12wherein pH of the aqueous solution of the anionic organic polymer havingat least one aromatic group is adjusted to a pH of at least 8 prior tomixing with the silica-based particles.
 18. The process according toclaim 12 wherein the anionic organic polymer having at least onearomatic group polymer is a polyurethane, lignosulphonate, Kraft ligninor oxylignin.
 19. The process according to claim 12 wherein the aqueoussilica-containing composition has a negative charge density within therange of from 0.1 to 6 meq/g.
 20. The process according to claim 12 withthe proviso that the composition contains substantially no sizing agent.